1. Field of the Invention
The present invention relates to a photo mask for transferring a mask pattern to a substrate by exposure to ultraviolet rays and a method for controlling the photo mask.
2. Description of the Related Art
Conventionally, even in the case of manufacturing a simple semiconductor device, several times of photolithographic processes have been repeatedly conducted, and when manufacturing a complicated ULSI, sometimes several ten times of photolithographic processes have been repeated. In this photolithographic process, a photo mask on which a predetermined pattern is formed must be prepared for every process.
If a foreign substance is attached to or formed on a photo mask used for the photolithographic process, an erroneous pattern is transferred onto a wafer on which the pattern is to be transferred. In a semiconductor device, this may lead to short-circuiting between circuits or breaks within circuits caused by any foreign substances created on the photo mask. Therefore, the so-called pellicle film is used to protect the photo mask in question to prevent foreign substances from attaching directly to the photo mask. The pellicle film prevents a foreign substance from attaching to a mask pattern formed on the photo mask and allows exposed light to penetrates without attenuation. The pellicle film will be briefly explained below.
FIGS. 7A and 7B are schematic block diagrams showing a conventional photo mask, FIG. 7A shows its plan view and FIG. 7B shows its sectional view.
In FIGS. 7A and 7B, a pellicle film 2 covering a mask-pattern-forming region 4 on which ultraviolet rays 10 irradiates at exposure is disposed in a photo mask 1. In a case where a foreign substance is attached to the pellicle film 2, since the position of the foreign substance deviates from the pattern imaging surface 8 (hereinafter referred to as a mask-pattern-forming surface) of the photo mask 1 by a height of a pellicle frame 3 made of metal or quartz, an image of the foreign substance is not built up on a wafer onto which the mask pattern is transferred, so that only required patterns 6 and 7 are focused into an image to be transferred. In short, it is made possible to use the photo mask even a foreign substance exists on the pellicle film 2. A photo mask using such a pellicle film is disclosed, for instance, in Patent Document 1.
[Patent Document 1]
Japanese Patent Application Laid-open No. 2000- 267261
[Patent Document 2]
Japanese Patent Application Laid-open No. Hei 11- 195585